120 



BRIDGMAN. 



SO that a superpressure of 5000 kgm. will not start it. At 200° a 

 small transition was found at about 2000 kgm., so small that I had to 

 repeat the work before I could be sure of it. If the transition had 

 been at 1000 instead of 2000, it would have been so near the end of 

 the stroke that it would have been missed altogether. This experience 

 shows that by making runs out to 12000 at 20° and 200° one cannot be 

 sure that there are no transitions in the region unless it is certain that 

 there are no transitions at atmospheric pressure between 20° and 200° ; 

 it is not sufficient warrant for the absence of a transition at atmospheric 

 pressure, even for a common chemical, that no one has noticed it and 



6 



Pressure, kgm. /cm. ^ x 10^ 

 Potassium Acid Sulfate 



Figure 14. Potassium Acid Sulfate. 

 and temperatures. 



The observed equilibrium pressures 



tabulated it. It is possible, therefore, that some of the substances 

 which I have examined for transitions without result may really have 

 transitions, since I have always assumed that if a substance has not 

 been tabulated as polymorphic it has no transition at atmospheric 

 pressure. I have found one or two other examples of new phases at 

 atmospheric pressure not known before. 



The equilibrium values of pressure and temperature are shown in 

 Figure 14, the values of Av in Figure 15, the computed values of latent 

 heat and change of internal energy in Figure 16, and the collected 



